1. Field of the Invention
The present invention generally relates to the storing of data on magnetic tape media and, more particularly, to tape heads for writing data to and reading data from magnetic tape media using a linear format.
2. Relevant Background
The market for mass storage devices is growing at an ever increasing rate with the sales of high-performance computers penetrating numerous industries ranging from financial institutions to oil exploration companies. The processing power of these high-performance systems, and the data they generate, are increasing faster than the ability of storage devices to keep pace. The problem of data storage and rapid retrieval is particularly pronounced in computational-intensive applications which create huge amounts of data that need to be accessed in seconds rather than minutes, hours or even days.
Magnetic disks remain the preferred media for direct access to frequently used files because of their fast access times. However, because of their high cost per-unit of storage and limited capacity, magnetic disk recorders are prohibitively expensive and therefore impractical for large-scale data storage. With the advances in magnetic tape technology, tape based systems remain the preferred choice for mass data storage. In addition to cost, magnetic tape exceeds the storage density of almost any other medium, at least from a volumetric standpoint, because tape is a much thinner medium than, for example, magnetic disks, and tape can be tightly packed.
Magnetic tape (e.g., recording tape) is a magnetic recording medium made of a thin magnetizable coating on a long, narrow strip of plastic which is typically stored in the form of a spool on a cartridge or cassette. The tape media contacts the surface of a linear recording head (e.g., tape head, tape head module, etc.) of a tape drive as the tape is transported from one reel to another. During write operations, a write transducer (e.g., write element) converts electronic pulses to magnetic signals that record a band (or track) of data onto the media as it travels across the head surface. The orientation of the write transducer (e.g., the longitudinal axis of the write transducer) is such that it is perpendicular to the travel of the media and the resultant magnetic transitions are thus written parallel to the travel of the media.
To enhance the data transfer rate of the tape drive, the linear recording head typically utilizes an array (e.g., set, span) of write transducers (e.g., 16 devices, 32 devices, etc.) that simultaneously record/write data to the media. The array of write transducers is oriented perpendicular to the direction of motion of the media (e.g., the travel of the media). When the entire length of recording tape has been run over the head (usually several hundreds of meters or more), the position of the head is shifted slightly relative to the media (e.g., laterally relative to a width of the media), the direction of the tape transport motion is reversed, and a new set of data bands are recorded onto the media adjacent to the ones previously written. This process is repeated multiple times resulting in numerous data tracks being written to the tape media. In the case of an approximately 12.5 mm wide recording tape, for instance, hundreds or thousands of data tracks may be recorded across the width of the tape.
When the data is read back from the media, read transducers located on the recording head are used to detect the magnetic transitions written to the tape and convert them to electronic signals. For linear recording, the width of the read transducer is typically smaller than the width of the written data track; doing so creates a “guard band” that allows for some positioning error between the centerline of the read transducer and the centerline of the written track of interest to occur without having any region of the read transducer go outside of the written data band. The positioning error is caused by system variations (e.g., servo positioning error, tape guiding error, manufacturing variations, temperature and humidity effects on the media and drive components, etc.) that are minimized but typically cannot be completely eliminated. Like the write transducers, each read transducer (e.g., its longitudinal axis) is oriented perpendicular to the direction of travel of the tape media as well as perpendicular to the data band being read.
For instance, FIG. 1 is a close-up simplified schematic plan view of a read transducer 708 reading data tracks 704 from a magnetic tape 700 according to a conventional design. Each data track 704 is written parallel to one of first and second opposite directions of motion 702, 703 of the magnetic tape 700. Accordingly, a longitudinal axis 712 of the read transducer 708 is oriented perpendicularly to the first and second opposite directions 702, 703 of motion of the magnetic tape 700 as well as perpendicularly to a particular data track 704 so the read transducer 708 can read the data track 704. The width of the read transducer 708 (i.e., the length of the read transducer 708 along the longitudinal axis 712) is smaller than the width of each written track 704.
In the event that a region of the read transducer 708 goes outside of the targeted written track 704, the read transducer 708 will read signal from the neighboring written track 704 as noise. As the read transducer 708 goes further off track, the amount of desirable signal decreases and the amount of noise signal increases, causing the signal to noise ratio to decrease dramatically. However, as the width of the read transducer 708 gets smaller (e.g., with reduced track widths), the amplitude of the detected signal also gets smaller. As there exists a certain level of inherent system (electronic) and media noise, decreasing the width of the read transducer 708 thus causes the signal to noise ratio to decrease as well. However, a robust data storage system requires a large signal to noise ratio. The design of the read transducer 708 for conventional linear tape storage systems therefore involves a balance between making the width of the read transducer 708 as large as possible to maximize the detected signal while keeping it small enough to provide an adequate positioning error guard band.
With each new generation of tape storage device, it is desirable to increase the amount of data that is stored on a cartridge of magnetic tape. One way of achieving increased data storage is to increase the number of data tracks that are written on the tape which necessitates making each written track width smaller and thus reducing the width of the read transducer. In this regard, striking a balance between read transducer amplitude and positioning error guard band becomes more difficult to achieve with each successive generation of tape data storage system.
One manner of increasing the signal to noise ratio is by dispensing with the guard band between the width of the written track and the read transducers altogether, such as through the use of “azimuth” recording in which bands of data are written at a slight angle (e.g., azimuth) to parallel (to the direction of media travel). Adjacent tracks are written with an azimuth angle of opposite sign (i.e., one track is written with a positive azimuth, the next with a negative azimuth, the next with a positive azimuth, etc.). A read transducer with the same azimuth angle as the written data can read the intended data without problem.
For instance, FIG. 2 is close-up, simplified schematic plan view of a read transducer 808 reading data tracks 804 from a magnetic tape 800 according to another conventional design. The data in each data track 804 (where the data is represented by the arrows in the data tracks 804 in FIG. 2) is written at an azimuth angle α to one of first and second opposite directions of motion 802, 803 of the magnetic tape 800. As shown, the read transducer 808 (its longitudinal axis 812) is oriented at the azimuth angle α relative to the perpendicular to the direction of motion of the magnetic tape so that the longitudinal axis 812 of the read transducer 808 is oriented perpendicularly to the data of the data bands 804 being read. If the read transducer 808 goes off track to an adjacent track 804 written with the opposite azimuth angle α, destructive interference is created that effectively cancels any corresponding noise. Hence, the width of the read transducer 808 (i.e., the length of the read transducer 808 along its longitudinal axis 812) can be as large as the written data track (or even larger as shown in FIG. 2) free of incurring any signal to noise degradation.